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1985 2.8 Carb Adjustments

ford4wd08

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Can someone please explain to me the choke adjustments on the '85 2150A carb?

I made slots in the shear torque screws so I could move the choke thermostat and now the choke will shut completely when it is cold and I adjusted the vacuum choke pull off with the correct sized drill bit and it starts very well now when cold.

If it idles for a while, it will begin to stumble and little and sometimes stall.

I understand that when the thermostat moves the choke open enough the screw will catch in the notch and prevent it from shutting until the accelerator is depressed when the engine is cold again to close the choke fully.

I guess my question is, what is the purpose and what adjustment am I supposed to make to the number 5 in the image below? I read the carb rebuild instructions, but I'm not sure exactly what it is telling me to do.

@RonD I'm guessing you know.
 

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Uncle Gump

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That is to get the fast idle speed screw to line up with the V on the cam. If yours lines up no adjustment necessary. That adjustment is only to place the screw on the V. To adjust fast idle speed you would use the speed screw.
 

RonD

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+1 ^^^

As far as the choke adjustment you may have it closing too much, so after it warms up the choke plate is not open enough

Cold engine, prop throttle open
Turn the Black Cap(choke spring adjustment) so choke plate is open a bit, not all the way closed, but mostly closed
Mark it(the cap), so you have a starting point

Release throttle
Start engine and see if it idles OK, high idle of course

Drive it to see if its stumbling under load, and to get it up to operating temp and see if its stumbling when warmed up

The point of the Choke plate on a carb is to restrict air flow which increases Ported Vacuum(vacuum above throttle plate), this causes more gasoline to be sucked in from idler and main jets, creating a Rich fuel mix needed on a cold engine.
As the cylinders/engine warms up choke plate needs to open a bit more so less Rich, and less Rich and less Rich until engine is warmed up enough to use regular 14:1 air/fuel mix

So it's a fairly precise adjustment of a grossly un-adjustable setup, lol

EFI Computers do this much better :)
 
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ford4wd08

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That is to get the fast idle speed screw to line up with the V on the cam. If yours lines up no adjustment necessary. That adjustment is only to place the screw on the V. To adjust fast idle speed you would use the speed screw.
+1 ^^^

As far as the choke adjustment you may have it closing too much, so after it warms up the choke plate is not open enough

Cold engine, prop throttle open
Turn the Black Cap(choke spring adjustment) so choke plate is open a bit, not all the way closed, but mostly closed
Mark it(the cap), so you have a starting point

Release throttle
Start engine and see if it idles OK, high idle of course

Drive it to see if its stumbling under load, and to get it up to operating temp and see if its stumbling when warmed up

The point of the Choke plate on a carb is to restrict air flow which increases Ported Vacuum(vacuum above throttle plate), this causes more gasoline to be sucked in from idler and main jets, creating a Rich fuel mix needed on a cold engine.
As the cylinders/engine warms up choke plate needs to open a bit more so less Rich, and less Rich and less Rich until engine is warmed up enough to use regular 14:1 air/fuel mix

So it's a fairly precise adjustment of a grossly un-adjustable setup, lol

EFI Computers do this much better :)
Seems to do fine when it is warmed up and driven.

It is only when I leave it running in the driveway that it get smother out and die. I only press the pedal once, it starts, and I leave it for a little bit.

I will take pictures of it cold and after driving and warming it up tonight when I get home.

It would absolutely not start unless the choke plate is completely closed when I was messing with it before. With the vacuum pull off it would start right off and run fine.
 

ford4wd08

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I looked at it warmed up the other day and it appears to rotate the choke plate to near 90 degrees or vertical.

I know EFI is better at this, but I'm so close to driving this thing as a daily driver. My Eco-boost let me down and required two new cylinder heads at 55,000 miles.... trying to keep the miles of it and go fight the daily drive with my carbed engine lol
 

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You may have the choke wound up to tight...

When it fully warms up ensure the choke is fully opened. What RPM do you have the fast idle set at?
 

ford4wd08

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You may have the choke wound up to tight...

When it fully warms up ensure the choke is fully opened. What RPM do you have the fast idle set at?
I have it set at just enough tension to keep it closed (this is based on an ambient temp below 50 degrees outside). It could be held a little bit tighter when colder.

I have no idea on the RPM for fast idle or how to set it... Maybe that would have been a better question to ask. I don't have a tach on this rig either.

I think it is time for a video of a start. Helped out before this summer!
 

Uncle Gump

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I looked at it warmed up the other day and it appears to rotate the choke plate to near 90 degrees or vertical.

I know EFI is better at this, but I'm so close to driving this thing as a daily driver. My Eco-boost let me down and required two new cylinder heads at 55,000 miles.... trying to keep the miles of it and go fight the daily drive with my carbed engine lol
Near 90 degrees isn't good enough. When warm the choke plate should basically pinned full open.
 

ford4wd08

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Near 90 degrees isn't good enough. When warm the choke plate should basically pinned full open.
I think it is close to 90, I'll have to check again. The thermostat spring doesn't have enough tension to keep it pinned I don't believe. It could be wearing out too.

This is also on an 85 with the feedback carb when they didn't want people adjusting the chokes. I have no mark to indicate where it was set on the housing and it had shear bolts. I was the first one to ever adjust it because it wasn't closing fully and letting the engine start at cold temps.
 

Uncle Gump

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Temps at 50 degrees wouldn't require full choke closed with a couple pumps on the accelerator. I would set the choke pretty loose if 50's are your lows.

Here is the real deal... carbs and an engine with a carb are really finnicky. This will take some testing of not only your choke settings... but your routine in starting.
 

ford4wd08

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Temps at 50 degrees wouldn't require full choke closed with a couple pumps on the accelerator. I would set the choke pretty loose if 50's are your lows.

Here is the real deal... carbs and an engine with a carb are really finnicky. This will take some testing of not only your choke settings... but your routine in starting.
Temps here swing alot, from near 0 degree lows and 50 degree lows all in the same week. The day I was working on it last, it was down in the 30s that night and high of a 50.

I could not get the engine to start at all without having the choke plate closed all the way when it was below 50 degrees. That is why I moved it to tighter. Now it seems to start fine.

I do remember as a teenager pumping the gas pedal twice and it would fire off, but the BII has been through a lot since then, including me working on it!

I am finding your statement in bold to be very true.....
 

ford4wd08

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So how do I adjust the fast idle and all if need be? I assume I need some sort of tach to tell me where I am at?
 

Uncle Gump

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Fast idle speed screw is item 4.

If your truck warm idles at say 750/800 rpm... think about 400 to 500 more when cold and the choke snaps closed... and you fire it up. When on the choke and fast idle cam... the speed will increase as it warms up which would end up about double your warm idle speed. But as it warms up.... blipping the throttle will allow it to drop off the fast idle cam... most likely in two steps. Depending on how warm it is.

I would take a good look down the throat of the beast... blip the throttle and ensure you have a good spray from the accelerator pump. If it looks weak you might have to pump it three or more time when really cold.

You just need to play with it a bit... I'm certain you can find the happy spot.
 

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If it "loads up" at warm idle then your idler jets may be the problem but I don't think they are adjustable on the 2150A feedback carb

It could also be your float is not adjusted correctly, at idle the float bowl may be overfilling a bit and leaking fuel into the engine(vent system), its a long shot
Pictures here: http://grantorinosport.org/bubbaf250/carb/carb02.html

This is not the "A" version but will have the float bowl Vent hose so check it for gasoline
 

ford4wd08

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If it "loads up" at warm idle then your idler jets may be the problem but I don't think they are adjustable on the 2150A feedback carb

It could also be your float is not adjusted correctly, at idle the float bowl may be overfilling a bit and leaking fuel into the engine(vent system), its a long shot
Pictures here: http://grantorinosport.org/bubbaf250/carb/carb02.html

This is not the "A" version but will have the float bowl Vent hose so check it for gasoline
I'll post a video of the start up later. I'm pretty happy with the progress from where I could not start it at all!

The float adjustment is not a bad idea, I had not considered that, it was overfilling at one time and I adjusted it.

Is there a good way to adjust the float wet? I think it would be the easiest with it installed and more accurate?
 

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